This proposal describes a 2-year research fellowship program, which will allow the principal investigator to develop an academic career in Pulmonary Medicine. The principal investigator has completed a Ph.D. dissertation, thorough residency training program in Internal Medicine and is currently training as a fellow in Pulmonary Diseases and Critical Care Medicine. The proposed research will investigate changes in the location and number of interstitial macrophage subsets in healthy human lungs and lungs from cigarette smokers. Dr. William Janssen, an expert in macrophage biology, will be the mentor and sponsor to the principal investigator during his scientific development in the field of myeloid biology. Dr. Janssen is an exemplary faculty member in the Pulmonary and Critical Care Medicine Division at National Jewish Health and the University of Colorado. The overall research goal of this proposal is to determine the influence of prolonged cigarette smoke exposure on three subpopulations of human pulmonary interstitial macrophages. Further, this project will define the native location of interstitial macrophages in healthy human lung tissue. We hypothesize that cigarette smoking will increase the total number of interstitial macrophages in human lung and will do so specifically within the tissue surrounding the small airways. We will characterize changes to the overall number and relative frequency of interstitial macrophage subsets in the lungs of smokers using flow cytometry. Further, we will use rigorous, design-based stereology to analyze immunofluorescently-labeled histology samples from human lungs to quantitate the location of macrophage subtypes as in proximity to airways, alveolar interstitium or vessels. Determining how interstitial macrophages are influenced by cigarette smoke will provide novel insight into the effects of cigarette smoking on lung biology and create a new avenue for future researchers to pursue therapeutics. Further, defining the native location of interstitial macrophages in healthy human lung will likely have applications to a variety of lung conditions beyond cigarette smoking. This work will also serve as the basis for future work as the principal investigator moves from fellowship, to junior investigator, to independent researcher.